Some of what you are seeing in the superiority of the Oly is an artifact of the E-M5 under-rating its ISO by about a full stop across the range (i.e. ISO 1600 on the camera is actually only 782)

Hi Scott, that's an oft-repeated mantra, but it is a misconception - one that DPReview have been very specific in countering - I will include some links to official DPReview statements at the end of this post.

The ISO 12232:2006 standard(Exposure Index Standard) only applies to the sRGB output of a camera (practically, the out of camera JPEGs). It says nothing about the RAW files, and the 'under-rating' you mention here is only seen in the RAW files. As such, that 'under-rating' is allowed by the ISO standard. Meaning, in effect, that it's not an under-rating at all.

While the DxO 'Measured ISO' numbers are very helpful for photographers and consumers who take the time to understand what they mean, they have nothing to do with actual ISO, as defined by the one and only standard that counts. DPReview has also been specific in stating that it's improper to mix the DxO numbers up with actual ISO numbers.

It gets worse as you go higher. This is why it looks so clean compared to the competition at any "equivalent" ISO. The GH2 also under-rates but not nearly as much. The lowly G5 is very close to spec.

This is also a commonly-held misconception, but it is also incorrect (and has also been directly addressed and contradicted by DPReview employees).

I suggest that you read the following statements from Andy Westlake (Technical Writer at DPReview), who took the time to explain some details about DPReview's testing regime and ISO, with the E-M5 tests and measurements as the original grounds for the discussions that were started.

To the OP: Scott's explanation for the E-M5's apparent superiority is technically incorrect, which fact is backed up by official statements from DPReview employees. The superiority you are seeing is actual, and cannot be explained away by any supposed 'tricks' performed by Olympus (Olympus has performed no tricks w/r/t ISO, as a matter of fact, according to the ISO standard), although many try to do exactly that, anyway.

Regarding the feel of the E-M5: My hands are average size. I use the camera without a grip and am very comfortable with it. I also like the fact that there are multiple grips from different makers available, and that, even if I decide to buy a grip at some time, I can always remove it if I want to go back to a very small camera that, with a pancake affixed, will easily fit in a jacket pocket.

Good luck finding a camera that works for you - the E-M5 and GH3 are both excellent choices, IMO!